A fair amount, in some cases - fire lookout towers, present and past. Most of these would have been erected early in the 20th century, and of course they were painted. I doubt anyone specified lead free paint, if they even knew of suvh a thing.

The fire tower in which I worked the summer of 1957 was mostly steel, but there were painted elements within the cabin. The typical lookout was a frame structure about twenty feet square, sometimes with ancillary buildings.